Sera from vasectomized men will be examined for the presence of circulating immune complexes and alterations in the complement system. These sera will serve as a model with which to determine possible consequences of sperm immunization. In addition, we will identify in the sera of men and women with unexplained infertility those sperm autoantibodies that circulate in the bloodstream either free or as antigen-antibody complexes. Immune complexes will be purified and their ability to activate complement will be determined. Following immune complex dissociation, its antigen, antibody and complement components will be identified. The results will further our understanding of humoral immunity to sperm components and are thus relevant both to the development of new contraceptive methodologies and to the treatment of immunological infertility.